Oscillation damping device



April 18; 1950 A. HEISIN G 2,504,329

OSCILLATIQN DAMPING DEVICE Filed April 5, 1944 PHASE SHIFT Y 0 PER SECTION LOW HIGH FREQUENCY FREQUENCY CUT -OFF CUT -0f7-' INVENTOR R! A. HE/S/NG ATTORNEY Patented Apr. 18, 1950 UNITEDJ- STATES: PATENT OFFICE 2,504,329 OSCILLATION DAMPING DEVICE Raymond A. HeisingQSuinmit, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a-corporation of New York Application April 5, 1944, Serial No. 529,633

10,000 megacycles per second or higher.' Difliculty has sometimes arisen due tothe tendency of a system to generate diiferent fre quencies'from time to time and, upon occasion, to shift erratically and unpredictably from one frequency to another. 4

This difficulty has its origin in a well-known property of coupled oscillatory'systems, namely, that a plurality of elements, even if all are resonant at one and the same frequency, form,.

when coupled together, a multiply-resonant system having a plurality of resonant frequencies, which are generally as numerous as the individual resonators comprising the system. The multiple resonant frequencies are distributed over a band.

of frequencies in the neighborhood of the resonant frequency of the individual resonators when the latter are tuned alike or nearly so. Under suitable conditions of excitation, the system may plurality of resonant elements in 9 Claims. (Cl. 315-40) ferred mode. If operation then tends to occur in a non-preferred mode or at such a. frequency that phase difierences arise between the portions so 'quencies, reaching at the present time to 3,000 to connected by resistances, currents will arise in the resistances and the resulting power loss or damping will tend to prevent operation. However, for the preferred mode of oscillation no such loss is introduced. Connectors introduced for, the purpose of preventing operation in non-preferred modes are known inthe art as mode-locking straps. 1

In accordance with the invention, resistive connections are made between certain points orpoles in the individual circuits of a multiply-resonant system to introduce power loss should currents arise in such resistive connections due to phase difierence between thepoints or .poles' so connected, with the object of suppressing or preventing oscillations except at a desired one of the resonant frequencies of the system.

In the drawing, Fig. 1 is a schematic representation of a typical multiply-resonant system as used in certain types of magnetron;

Fig. 2 is a representation of a portion of the resonator of Fig. 1 as if unrolled;

Fig. 3 is a schematic representation of the equivalent electric circuit of the resonator of. Figs- 1 oscillate at any one or more of the resonant fre-r quencies and as conditions of excitation change, the operating frequency may also change. To

provide a reliable source ofa desired single'frequency, oscillations at the undesired resonant frequencies' should be suppressed under all operating conditions.

The combinationof a plurality or train of coupled resonant circuits or cavity resonators forms the equivalent of a band-pass filter having a numher of sections equal to the number of component...

resonators. From filter theory, it is known that a network of this type has a certain phase shift per section which varies over the transmission band.

With this view'of the operation of the resonating system, if it is desired to restrict the operation to a single predetermined frequency'or to a preferred mode of oscillation, this may be done by connecting ohmic resistances between pairs of points or circuit portions for which no phase:

difference arises during oscillations of the pre- Fig. 4 is a simplified equivalent circuit derived from the circuit of Fig. 3;

Fig. 5 is a graphical representation, of the phase shift-frequency relation in the type of circuit shown in Fig.4;

Fig. 6 is a schematic circuit diagram showing the addition of .intercircuit resistances in the network shown in Fig. 4;

Figs. 7 and 8 are schematic representations showing respectively two ways of connecting intercircuit resistances in a resonating s'ystemsuch as shown in Fig. 1. l Fig. 1 is the conventional schematic representation of a resonating system of the general type employed in a magnetron oscillator such as is disclosed in U. S. Patent 2,063,342, issued December 8, 1936 to 'A. L. Samuel; The resonator comprises a solid anode portion I ll such as a block'of conductive material pierced or perforated to definev a plurality of resonating cavities l I connected by channels 12 to a reaction space 13 containinga cathode M. It is well known that a system er the type shown in Fig. 1, when-properly excited,

will oscillate electromagnetically as a multiplyresonant system. The conductor-shown in Fig; 1

is represented as being unrolled in Fig. 2 for convenient comparison with the equivalent circuit representation in Figs. 3, 4, and 6.

At the high frequencies of microwave operation, it is well known that the cavity H is capable of internal resonance wherein capacitances formed between various portions of the walls of the cavity resonate with the inductance of the walls. In Fig. 1, equivalent capacitances C1 are indicated in dotted :lines. #At high frequencies the currents will reside principally. in a'ithin conductive layer close to the cavity H and to the coupling channel [2, although at lower frequencies entire segments, such as indicated at I separating adjacent cavities may conuuctcun rents. segment I5 is represented aby .L. i :The;-i-nner:.-surfaces of the channel I2 provide ascmewhat: concentrated capacitance C2 which. serves to couple reactively between adjacent "segments "T5. The

above considerations lead to the equivalen t'ciref cuit for the system or Fig. 2 as represented .--schematica-lly. in Fig.3. lIhe adjacent iparallel .elemen-ts-in Fig. 3-maybecombinedas indicated min Fig. 4- to 'form 'the'network. of a :well-known type of --band-pass .fi'lter. vfithehcuteoi t. frequency .-.'.at.the high frequency edge-of. the'Ifilterband is --known ii-om filter theory to be theresonant fre- -.quency of.-.the parallel combination ofQthe. .in- .ductance L with twice. thacapacitance C1. The other. cu't'off frequency isdetermin'ed by. the .carpacitance C2 resonatingin. series .with four. times the shunt combination of the inductance Land twice the capacitance ;Cl. Intheexample shown, ...with six resonant elements joined. in a. series or z'..in 'aIclosedItring with .the output-and the .input connected together, there willbela't least six reso- .nan't frequencies.

If Thephase shiftper section through a'deyice of .this type is indicated in Fig. 5." The .phase shift is 180 degreesrpersectionat the w. freque'ncy cut-oil and zero'at the high." frequency wh ch.

A..circuit ofthistype, resonating at the lowest frequency in its band will have maximum. potential difference 'across fall' the: C2. capacitances' and every second circuit will be substantiallyin phase. 'At the other frequencies; higher within the band,

somewhat less-than 1'80 degreesphase shift .will occur between 'nei'ghboringicircuit's untilat the high frequency end "of the band all-the circuits will oscillate substantially inv phase. .Fromiithis figure it will be evident thatfthe modesiof'oscillation will generally differ in respect to the phase distribution along the "series of elements.

' 'It is commonly found desirable in the operation. of circuits of this type tc'fa'vcr the mode "-"ofoperation in which neighboring polesc'perate in oppositephase, corresponding to'ithecondition at the low frequency-endiof'thet'bandfl' In order to restrict the operation t0this particular frequency; "provision may be made as. shown in "Figs. 6, land 8 by'connectingtogethefthose pairs of circuit portions which it is desired to maintain in continual phase agreement." The connection is preferablymade by means-of re- "sistances. 'If operationwhentends' to occur at 'such"'frequencies that phase differences occur between the resistance-connected points; power losses willoccur in the resistances and suppress "or prevent --oscillations. Ali the frequency at which the resistance" connected points are in phase, no loss isintroducedfi Resistances are "preferable for such-connections as-they=-introduce an actual loss when current traversesthem and thus definitely tend to stop 'o'scillationsi Connecting by "wires or conductors which mainly The efiective inductance .of each anodes 4 comprise inductance or are without material amounts of ohmic resistance will not generally serve to prevent oscillation. In the case of purely inductive connectors, the inductance will gen- 5 erally be so great compared to other reactances in the circuit to which they are efiectively in parallel that they will fail to seriously influence the phase relations.

'Ass uming that it is desired to operate at the lovlowest frequency in the b'and, alternate or nonadjacent circuits may be connected by resistors .HB and I! as in Fig. 6.

.Fig. 7. .shows another scheme of resistance in- 'ter-ccnnectiens to suppress oscillations at freldquenciesmther. than the lowest frequency in the Inifth'is arrangement alternate segments desire-connected by resistors I8, l9 and 20, as

shown. .In casethere are eight or more resonant circuits", four or more resistors may be employed gosinraihdbvious extension of the arrangement of Fig. 7.

r :Fig. 8 shows-another :way in which. the-resistance connections may be made. i in this arrangement, 'the resistorsiare inductively coupled. to :the

resonant cavities as shown. A resistor 2 I has. one

terminal connected to =arrrinductive-loop 22 extendingainto one' of the-resonant cavities and :the

a other terminal connected to the adjacent cavity ;by. means of -an:inductive:;loop.23 of reverse polarity with-respect to loop 2 2w I Dtherresistors :such as resistor :24' 'may' be connected in a similar manner, the resistor 24 being shown coupled; by 'cmea-ns'of theloop 23 atone end and by. means of =another loop.-2'5 at the opposite end, theloop-25 *beingcoupled to thencxt adjacent cavityinop- .qaosite-polarityto the loop 23. iT-he, system of connection in Fig. 8- maybe extendedzto" several,

-- or :all-rof the individualcavities. The. connec- 'tions from thea-inductive'loops may -be brought 40 out through the side ofitheiresonator and tuning devices or transmission lines may be :illCOT-DO- mated, if desired-into the connecting; leads. The 1 connections .are :.-such' that when the magnetic .---fields.imtheresonators H are in phase no potential dillerences will occur acrossth'e resistors.

--VVhat is claimed is:

-l=. Ananode comprising ab l'ock ofconductive um'aterial perforated to define a train-of coupled "cavityresonators; forming. a system having a 5 .plurality-.-of modes- 0felectromagnetic oscillation including a preferred-mode in which adjacent =cavit-iescscillate =in phase.- opposition, and a resistor. coupled to two adj a'centresonant cavities f by couplingsof. opposite polarity whereby dampmg is: introduced into. both" of said adjacent reso- :nant-.cavities selectively to suppress non-pre- 'ferred modes: of oscillation.

2=1The combihatioirasain .claim 1 having a .plurality of resistorsreacnz-ccupled to two adjago-rcent cavity resonators'bys-couplings of opposite polarity.

3.. :An annd'e block'of conductive material per- :iorated tmdefine a plurality ofcavity resonators connected by :indlviduallchahnelsto a reaction 5" space and. having. conductive anode segments betwe'ena'djacent cavity-resonators, and a modelocking strap connected between'two anode segmerits; said mode l'Ocking: strap comprising. a

damping resistor, the resistance of which is com- -:parable in impedance value. to the impedance value of the inductance. ofysaid strap in the operating frequency rjange of-said anode block.

4. The 'combination accordin to claim 3 in which-the mode-locking strap is connected be- 75tween two non-adjacent .an'ode segments.

5. The combination according to claim 3 in which the mode-locking strap connects a pair of alternate anode segments.

6. An anode block of conductive material perforated to define a plurality of cavity resonators connected by individual channels to a reaction space and having conductive anode segments between adjacent cavity resonators, and a plurality of mode-locking straps connecting a set of alternate anode segments, each said mode-locking strap comprising a damping resistor the resistance of which is at least as great in impedance value as the impedance value of the inductance of said strap in the operating frequency range of said anode block.

7. An anode block of conductive material perforated to define a plurality of cavity resonators connected by individual channels to a reaction space and having conductive anode segments between adjacent cavity resonators, and a set of mode-locking straps connecting a set of alternate anode segments, each said mode-locking strap comprising a damping resistor the resistance of which is at least as great in impedance value as the impedance value of the inductance of said strap in the operating frequency range of said anode block.

8. An anode block of conductive material perforated to define a plurality of cavity resonators connected by individual channels to a reaction space and having conductive anode segments between adjacent cavity resonators, and a closed loop circuit comprised of a plurality of modelocking straps in serial connection, the junction points between said straps being connected respectively to alternate anode segments, each said mode-locking strap comprising a damping resistor the resistance of which is of the same order of magnitude in impedance value as the impedance value of the strap in the operating frequency range of said anode block.

9. The combination according to claim 8 in which the number of mode-locking straps is equal to one-half the number of anode segments in the anode block.

RAYMOND A. HEISING.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,079,248 Fritz May 4, 1937 2,136,101 Fritz Nov. 8, 1938 2,224,122 Ramo Dec. 3, 1940 2,242,888 Hollmann May 20, 1941 2,247,338 Ramo June 24, 1941 2,270,160 Berger Jan. 13, 1942 2,270,777 Bayer Jan. 20,1942 2,408,235 Spencer W Sept. 24, 1946 2,412,772 Hansell Dec. 17, 1946 2,417,789 Spencer Mar. 18, 1947 2,422,465 Bondley June 17, 1947 2,422,695 McRae June 24, 1947 2,446,572 Bull Aug. 10, 1948 FOREIGN PATENTS Number Country Date 103,231 Australia Feb. 9, 1938 

